Re: [RFC PATCH] crypto: crc32c-pclmul - Use pmovzxdq to shrink K_table

Tim Chen
2014-05-30T17:56:36Z

On Thu, 2014-05-29 at 21:16 -0400, Dave Jones wrote:
> On Thu, May 29, 2014 at 06:07:16PM -0700, Tim Chen wrote:
> > On Thu, 2014-05-29 at 19:54 -0400, George Spelvin wrote:
> > > Sorry for the delay; my Ivy Bridge test machine isn't in my
> > > office and getting to the console to tweak the BIOS is a
> > > bit of a bother.
> > >
> > > Anyway, i7-4930K, turbo boost & hyperthreading disabled,
> > > $ cat /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor
> > > performance
> > > performance
> > > performance
> > > performance
> > > performance
> > > performance
> > >
> > > Oddly, though, CPU speed still seems to be fluctuating:
> > > $ grep MHz /proc/cpuinfo
> > > cpu MHz : 1255.875
> > > cpu MHz : 3168.375
> > > cpu MHz : 3062.125
> > > cpu MHz : 1468.375
> > > cpu MHz : 1309.000
> > > cpu MHz : 2212.125
> > > $ grep MHz /proc/cpuinfo
> > > cpu MHz : 1255.875
> > > cpu MHz : 2690.250
> > > cpu MHz : 1255.875
> > > cpu MHz : 2530.875
> > > cpu MHz : 2212.125
> > > cpu MHz : 1521.500
> >
> > This is odd. On my Ivy Bridge system the CPU speed from /proc/cpuinfo
> > is at max freq once I set the performance governor.
> > The numbers above almost look like
> > the cpu frequency is fluctuating and an average is taken.
> > What version of the kernel are you running? Is
> > CONFIG_CPU_FREQ_GOV_PERFORMANCE compiled in?
> >
> > Does /sys/devices/system/cpu/cpu?/cpufreq/scaling_cur_freq
> > also changes?
> >
> > Can you check what are the available governors in your system
> > and available frequencies?
> >
> > cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
> > cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
> >
> > If userspace governor is available, you can try set the governor
> > to userspace, then pin frequency to 3400 MHz (assuming that's your
> > max) with command like:
>
> intel_pstate overrides any governor choice you make through sysfs.
>
> Dave
>

Dirk,

Wonder if this the right behavior for intel_pstate that when I set the
governor to performance, intel_pstate driver still adjusts
the cpu frequencies around?

Turbotstat also confirms that the frequencies are not at max,
even though the max_perf_pct and min_perf_pct are both set at 100.

I ran on my HSW system with 3.15-rc7 kernel and see similar
issue that Geroge reported.

It is really a pain when we need to do performance benchmarking and
need to have a constant cpu frequency.

Thanks.

Tim